A Trace of Memory

The Bad Astronomer describes how advances in the mathematics of Loop Quantum Gravity has allowed theorists to examine what happened at T=0: the moment of the Big Bang.

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It’s been thought for sometime that there may have been some previous Universe that existed "before" ours. This is a difficult idea, because in the Big Bang model, space and time were created in that initial moment. But if Bojowald’s solutions are correct, it leads the way to understanding this previous Universe. It was out there, everywhere, and it contracted. Eventually it became an ultradense, ultrahot little ball of space and time. At some point, it got so small and so dense that bizarre quantum laws took effect — things like the Uncertainty Principle, which states that the more you know about one characteristic of an object (say, its position) the less you know about another (its velocity). There are several such laws, and they make it hard — impossible, really — to know everything about the universe at that moment.

What Bojowald’s work does, as I understand it (the paper as I write this is not out yet, so I am going by my limited knowledge of LQG and other theories like it) is simplify the math enough to be able to trace some properties of the Universe backwards, right down to T=0, which he calls the Big Bounce. The previous Universe collapsed down, and "bounced" outward again, forming our Universe. No doubt the physical aspects of this previous Universe were somewhat different; the quantum uncertainties at the moment of bounce would ensure that. It may have been much like ours, or it may have been quite alien. In his equations, it’s the volume of that previous Universe that cannot be determined. How big was it? It may literally be impossible to ever know.